As is well known in the art, thin film magnetic heads used with data storage apparatus, such as disk files, typically comprise magnetic pole pieces and an electrically conductive coil structure disposed between the pole pieces. The tips of the pole pieces define a transducing gap for coaction with a magnetic medium, such as a magnetic disk that rotates close to the transducing gap of the head. The pole pieces interconnect at a back gap closure. A polished ceramic substrate having a thin insulation layer thereon, which is lapped and polished, supports the different layers which are deposited to form the magnetic transducer. To prevent electrical shorting, insulating layers are provided between the coils and pole pieces.
During operation in the recording mode of a data storage device, such as a disk drive, current representing data signals is directed to the conductive coils. The current is converted to magnetic flux signals by the magnetic head or transducer, and the signals are recorded on the disk as it rotates adjacent to the nonmagnetic transducing gap. During the readout or playback mode, as the magnetic disk is rotated past the head, the recorded magnetic flux signals are sensed and are converted to current that flows through the conductive coils. Bischoff et al. U.S. Pat. No. 4,694,368 which issued on Sep. 15, 1987 describes a process of making a thin film magnetic head or transducer, and is incorporated herein by reference.
A significant problem that is experienced with thin film magnetic heads is the relatively high coil resistance or transducer resistance. The power I.sup.2 R (where I is current and R is determined by the value of coil resistance. Thus the higher the resistance) that is dissipated during the recording process is determined by the value of coil resistance. Thus the higher the resistance of the head coil structure, the higher will be the power dissipation and the greater the extent of thermal expansion of the components of the recording head and the recording apparatus. Thermal expansion adversely affects the recording operation. In addition, during the readout mode, the amount of thermal noise that is generated depends upon the level of coil resistance. This thermal noise is generated at the transducer level and will be amplified in the storage apparatus, resulting in an undesirable reduction of the signal-to-noise ratio of the recording process.
An important factor to be considered in the design of a recording head is the number of coil windings or turns which are used. Signal output is directly proportional to the number of turns. As narrower tracks are used on the disk surface, higher track density and higher data density make it necessary to use more coil turns in order to maintain an adequate signal level. If the signal being processed has a low amplitude, data errors may occur during the recording process.
Thin film heads typically have small geometries, when compared to prior art ferrite heads. In order to maintain a high efficiency for the thin film head, coil pitch had to become smaller and smaller, which resulted in an increase in coil resistance. Presently known thin film heads are characterized by an average resistance of about 30 to 40 ohms for a 34 turn head, and 40 to 50 ohms for a 42 turn head, by way of example. On the other hand, ferrite heads have a resistance of 5 to 10 ohms for a 30 turn head. The difference in resistance occurs because the larger ferrite heads are able to use conductive wires or turns with a 25.4 to 50.8 microns diameter, while the cross-section of a thin film head turn is about 3-4 microns.
One approach that has been considered for reducing the overall resistance of a thin film transducer is to make the coils wider. However, wider coils reduce the efficiency of the transducer because the yoke structure would necessarily have to be made too long. Another approach would be to make the entire coil thicker which has its limitations because of constraints that arise with the photoresist process. If the coils are too thick under the magnetic portion of the transducer, subsequent fabrication of the top pole piece becomes more difficult because of the increased step. Also, since there is a large difference in thermal expansion between the insulation material used for insulating the coils and the nickel alloy material used for fabricating the poles or magnetic portion of the transducer, the use of too much insulating material would adversely affect the performance of the recording head.
Another approach to realize lower transducer resistance is to use a different coil material having lower resistance. At present, transducer coils are made of electroplated copper having a resistivity in the range of about 1.8 to 2.2 ohms centimeter. Although silver has a lower resistivity of 1.59 ohms cm., the fabrication of silver coils is so complex that it would outweigh any advantage of a 3% reduction in resistance.